Louis was the oldest of 7 siblings.

18-year-old Felicite Tomlinson passed away Wednesday at her studio apartment in London. She collapsed from a heart attack, and someone in the apartment called for an ambulance … but after paramedics tried to revive her, she was pronounced dead at the scene.

Louis and Felicite were extremely close, regularly seeing each other when he was in London.

Felicite was a fashion designer and had more than 1 million followers on Instagram. It’s apparent from her Insta, she was heavy into fitness. She was planning to publish a book of her own poetry.

Louis has just pulled out of a performance on a BBC charity show, Comic Relief. The show was aired lived Thursday night, but Louis obviously had to back out.

We’re told Louis is with is family right now and he’s devastated. The One Direction singer lost his mother to cancer in December 2016 when she was only 43. He recently released a song called “Two of Us,” about him and his mom. The lyrics include, “You’ll never know how much I miss you/the day that they took you/I wish it was me instead.”